President Obama and former President Bill Clinton mark the 20th anniversary of AmeriCorps, which promotes volunteerism and community service, on the South Lawn at the White House in Washington on Sept. 12, 2014. (Associated Press) more >

Twenty years after President Clinton tackled gun control by drastically reducing the number of licensed firearms dealers in the U.S., President Obama is preparing to tackle gun control by increasing the number of licensed gun dealers.

The different approaches of the two Democratic presidents is just one sign of how the politics of firearms has been transformed, and of Mr. Obama’s scaled-back ambitions despite a string of high-profile gun massacres during his time in office.

With his gun agenda blocked in Congress, Mr. Obama is expected to announce executive actions imposing new gun regulations soon after the holidays. One of the most likely changes is a rule that would require dealers who exceed a certain number of gun sales each year to obtain a license from the Bureau of Alcohol, Tobacco, Firearms and Explosives and to perform background checks on buyers.

The action contemplated by the White House hinges on the legal definition of those who are “engaged in the business” of buying and selling guns for profit as their livelihood. Current law doesn’t set a total number of annual gun sales to qualify as a business, but Democratic lawmakers and gun control advocacy groups are urging the White House to issue the rule as a way to close the “gun show loophole” that allows firearms to be sold without background checks at such expositions.

Federally licensed gun dealers are required to perform background checks on all gun sales, and only people who are deemed to be “engaged in the business” of dealing in guns are required to get ATF licenses.

Whether or not such action would have any appreciable effect on gun violence, it’s essentially the reverse of Mr. Clinton’s far more direct response to gun crime in the mid-1990s.

Laws passed under the Clinton administration, such as the Brady Law and the Violent Crime Control Act of 1994, changed the licensing procedures for federal firearms licensees by increasing fees and requiring gun dealers to submit photographs and fingerprints as part of their applications.

Primarily because of the increased regulation, the number of federal firearms licensees dropped from about 282,000 in 1993 to fewer than 104,000 by 1999.

“The complaints from the gun-control groups [in the 1990s] were that there were way, way too many FFLs, and the government needed to crack down on and reduce the number of licensees,” said Lawrence Keane, general counsel of the National Shooting Sports Foundation, the firearms industry’s trade association. “Now all of a sudden, we’re hearing the gun control groups say there aren’t enough licenses, and everybody needs to have a license.”

Gun homicides reached a peak in the U.S. in 1993 at seven homicides per 100,000 people and steadily declined after that to 3.8 homicides per 100,000 people in 2000. Researchers are still trying to reach a consensus on the causes for the drastic decline.

Since 2000, the gun homicide rate has remained relatively flat, according to an analysis by the Pew Research Center. From 2010 to 2013, the most recent year for which data are available, the number of gun homicides has hovered between 11,000 and 12,000 per year.

Despite the reduction, most Americans think gun violence is on the rise. Pew’s survey in 2013 found that 56 percent of Americans believed the number of gun crimes had gone up compared with 20 years ago, while 12 percent said gun crimes had declined.

A Pew survey in July 2015 found that 85 percent of Americans (88 percent of Democrats and 79 percent of Republicans) favored expanded background checks for private gun sales and purchases at gun shows.

Blocked on the Hill

The Senate stopped an effort in 2013 to expand background checks on gun purchases. But Democratic lawmakers urged Mr. Obama last month to eliminate ambiguity in federal laws surrounding the term “engaged in the business” as it pertains to licensed firearms dealers.

“This type of action is not without precedent, as many states have provided this type of explicit guidance regarding which vendors engaged in retail sales in the state are required to collect states’ sales tax,” they wrote in a letter. “This change would be a positive step forward in closing the private sale loophole, a policy change that roughly 90 percent of Americans support.”

After Mr. Obama visited families of victims of the San Bernardino terrorist attack on Dec. 18, Dan Gross, president of the Brady Campaign to Prevent Gun Violence, called on the president “to use the full weight of his office to address an issue that is killing 32,000 Americans each year and keep guns out of the hands of the people we all agree shouldn’t have them.”

“President Obama now has the ability to follow through on the thoughts and prayers he offers today with meaningful action,” Mr. Gross said.

In a video message last week, National Rifle Association Executive Vice President Wayne LaPierre criticized “a government that would disarm us during the age of terror.”

“The greatest damage the terrorists could ever inflict upon us is disarmament at the hands of the political elites,” Mr. LaPierre said. “But we will never offer our right to survive as a fool’s ransom to the world’s killers.”

Gun regulations would fall on agencies to enforce, and some observers say the ATF isn’t prepared to regulate and monitor what could be an increase of as many as 100,000 federal firearms licensees.

“It will create an administrative problem for ATF in the sense that their budget does not provide for them to handle some huge increase in the volume of FFLs,” said Mr. Keane. “If ATF now has to manage 100,000 individuals, or whatever the number is, who have to get a license, that’s going to divert resources that ATF needs to be servicing industry, and it takes money away from ATF’s ability to do its law enforcement duties. So delays will grow.”

As the White House gears up to announce the executive action, some Republican lawmakers are taking steps to blunt the impact.

Sen. Rand Paul, Kentucky Republican, is pushing for a vote to restrict Mr. Obama’s ability to enact gun control regulations. He introduced legislation last month that would decree any executive action on gun control that either infringes upon congressional authority or potentially violates the Second Amendment as “advisory only,” unless Congress passes legislation to support it.

“In the United States, we do not have a king, but we do have a Constitution,” Mr. Paul said. “We also have the Second Amendment, and I will fight tooth and nail to protect it.”

The legislation is expected to be placed on the Senate calendar in January, although no vote has been scheduled.

Mr. Obama hasn’t issued executive orders on guns since January 2013, in the wake of the Sandy Hook school massacre in Connecticut.

In a posting on Facebook on the three-year anniversary of the shootings, Mr. Obama recalled meeting parents of the young victims.

“Three years on, how do we tell them that their Congress hasn’t done anything to prevent what happened to them from happening to other families?” Mr. Obama wrote. “The gun lobby is loud and organized in its defense of effortlessly available guns for anyone. The rest of us are going to have to be just as passionate and organized in our defense of our kids. America, this will change — but only when we stand up, together, and demand it.”